At present, in a wireless LAN, a communicating system using a 2.4-GHz band and a communicating system using a 5-GHz band are available and also in a mobile telephone, a communication system using a 0.8-GHz band and a communication system using a 1.5-GHz band are available.
Formerly, one communication device was able to communicate with another only in one frequency band system. In recent years, however, one communication device that can communicate in two frequency bands systems has also been developed.
Such a communication device that can communicate in a plurality of frequency bands needs to use a multi-band antenna capable of transmitting and receiving radio waves of a plurality of frequency bands.
Various types of multi-band antennas are available. For example, “Zukai idoutuushinyou antenna system” written by FUJIMOTO Kyouhei, YAMADA Yoshihide, and TUNEKAWA Kouichi, published by Sougou Denshi Shuppansha discloses an antenna shown in FIG. 6.
FIG. 6 is a plan view to show an example of a multi-band antenna in a related art. An antenna 100 has two antenna elements 104 and 106 made of conductors placed in parallel on a dielectric substrate 102. Power is supplied to the antenna elements 104 and 106 in parallel through a feeder line 108 divided into two branches at an intermediate point from a signal source (not shown).